As is well known, harvesters may be equipped with a variety of interchangeable gatherer units to suit particular crops or harvesting conditions. Corn heads are used with base units to permit the harvesting of corn. The corn head is a row crop device and so is equipped with a series of shrouds or snouts which function as divider points for guiding plants or stalks into the throats of the respective row units as the combine advances down the rows of standing crop. Gatherer chains then guide the stalks rearwardly relative to the corn head while stalk rolls pull the stalk down and corn ears are snapped from the stalk by deck plates. The gatherer chains convey the ears rearwardly and upwardly and deliver them to a trough having a cross auger extending laterally, immediately behind and spanning the row units. The auger rotating in the auger trough pulls the ears of corn to a laterally central region of the corn head. A central conveyor receives the ears and conveys them backwards through a hole on the rear wall of the corn head, then through a feeder house and then into the vehicle where the ears are threshed, and the corn kernels cleaned and stored. Many corn heads include optional chopping units each having a rotatable blade located beneath the stalk rolls for cutting and shredding the downwardly moving corn stalks which may then be left in the field to decompose. Corn heads include a frame, including a toolbar extending across the width of the frame to which row units and chopping units are attached. The row units and chopping units are driven by a laterally extending drive shaft that extends through all of the row units and chopping units.
During normal operation, one or more row or chopping units will occasionally become jammed with foreign material and stop operating altogether. When this happens, the drive shaft continues rotating, but is mechanically released from the stopped unit by disengaging a slip clutch that couples the drive shaft to the unit, thereby permitting the drive shaft to continue rotating even though the row unit or chopping unit is jammed. This clutch slippage cannot continue indefinitely, however, since a slipping slip clutch can overheat to destruction in just a few minutes during normal operation through the field. The clutch slips whenever the row unit or chopping unit is jammed, rubbing metal against metal. If this jammed row unit/jammed chopping unit condition is not detected, a clutch could burn up in as little as 5-10 minutes.
As a further complication, it is impossible for the operator to see whether clutches are slipping. The slip clutches are invisible from the operator station. The chopping units, if present, are disposed underneath the corn head where they cannot be seen and the row units are disposed underneath the covers or shrouds that guide the corn plants into the row units. The covers, sometimes called snouts, are not illustrated.
Typically, the only indication is the noise generated by the slipping clutch. Unfortunately, agricultural harvesters are noisy and it can be very difficult if not impossible to hear this clutch noise.
Row and chopping unit jams could be detected by using shaft speed sensors located at each of the row and chopping units. This solution, however, would require a sensor for each unit and considerably cabling to connect all the sensors to a single sensing system and therefore are not used in any production corn head.
U.S. Pat. No. 6,843,044 B2 discloses an arrangement for the detection of a crop jam in a front harvesting attachment or a harvesting machine having an overload clutch inserted into the driveline of a crop conveying element of the harvesting machine that interrupts the driveline, in the case that an established torque limit is exceeded due to a crop jam. The overload clutch, which may be a cam-controlled clutch, is inserted into the driveline of the conveyor arrangement between the conveyor arrangement and an articulated shaft that connects it with a gearbox providing its mechanical drive. The overload clutch separates the driveline of the conveyor arrangement when the torque transmitted by the overload clutch exceeds an established limit value determined by the overload clutch. Generally, the overload is caused by a crop jam in the conveyor arrangement. The slip clutch generates acoustic or mechanical vibrations. The detection arrangement is equipped with a sensor that can, if necessary, receive these vibrations and detects them with the use of an appropriate analog and/or digital signal processor. A control arrangement connected with the sensor can inform the operator of the harvesting machine acoustically and/or optically in case of a crop jam, or even take appropriate steps automatically to remove the crop jam, particularly turning off the drive of the crop conveying element, raising a hold-down arrangement of a pick-up or a reel of a cutter head, and/or reversing the drive of the crop conveying element.